Method of and composition for the treatment of scale

ABSTRACT

METHOD OF AND COMPOSITION FOR THE TREATMENT OF SCALE, PARTICULARLY CALCIUM SULFATE SCALE, USING A QUATERNARY TRIMETHYLALKYL AMMONIUM HALIDE, SULFATE OR HYDROXIDE CONTAINING 8 TO 20 CARBON ATOMS IN THE ALKYL GROUP INCLUDING MIXTURES.

3,579,445 METHOD OF AND COMPOSITION FOR THE TREATMENT OF SCALE Jack F.Tate, Houston, Tex., assignlor to Texaco Inc., New York, N.Y. NoDrawing. Filed June 24, 1968, Ser. No. 739,207 Int. Cl. C02b 5/06 US.Cl. 210-58 7 Claims ABSTRACT OF THE DISCLOSURE Method of and compositionfor the treatment of scale, particularly calcium sulfate scale, using aquaternary trimethylalkyl ammonium halide, acetate, sulfate or bydroxidecontaining 8 to carbon atoms in the alkyl group including mixtures.

This invention relates to a composition useful in treating oil and gaswells and to a method of using such composition for such treatment. Moreparticularly this invention is directed to a composition and methoduseful in the prevention and/or inhibition of the build-up ofundesirable inorganic mineral scale deposits in oil and gas wells, theirflow lines, auxiliary producing equipment, such as heat exchangers andcooling towers, as well as the producing strata in the vicinity of thewell bore. Additionally, the invention is useful in the prevention and/or inhibition of build-up of scale deposits in aqueous systemssusceptible to mineral scale formation.

The formation of objectionable scale deposits, such as calcium or bariumsulfate is rather Widespread in certain 7 production areas, and has beenattributed to several causes. One generally accepted theory of scaleformation is that of chemical precipitation resulting from thecommingling of two fluid streams each of which contains a concentrationof a particular ion such that when they commingle an unstable water isproduced. For example, in the case of calcium sulfate scale formation,one stream contains sulfate ions, and the other calcium ions in suchconcentration so as to produce an unstable water. The mixing of thesestreams at the well bore may result in the deposition of crystallinecalcium sulfate which gradually builds up on the Walls of the welltubing, for example, to a point where it may choke off fluid flow in thetube if remedial measures were not undertaken.

Another cause of the scale formation is attributed to the precipitationof scale material from potentially supersaturated solutions thereof.When the operating variables of temperature and pressure changeadversely, or solvent is allowed to evaporate, thus concentrating thesolutions, precipitation of the salt on the tubing and surroundingstrata occurs.

The use of strong alkali solutions for the removal of sulfate scale hasbeen proposed. It has been claimed that under certain favorableconditions of temperature and time, concentrated alkali solutions will,in some cases, provide a break-up of the built-up scale after relativelylong periods of treatment. If, for example, a calcium sulfate scale istreated with concentrated potassium hydroxide for comparatively longperiods of time, say from 24 to 72 hours, it has been claimed that awhite fluffy precipitate of calcium hydroxide will be formed. Thisprecipitate may then be removed by suitable mechanical means. Such amethod is obviously undesirable in that considerable periods of time areinvolved and the use of mechanical apparatus is expensive, and in somecases, either undesirable or mechanically impossible. Moreover, strongalkali is not effective in preventing or inhibiting the build-up ofscale deposits in well tubing, production equipment and the producingstrata about the bore hole.

3,579,445 Patented May 18, 1971 It is, accordingly, an object of thisinvention to provide a method of inhibiting and/or preventing thebuildup of scale deposits in gas and oil flow lines, auxiliaryequipment, well tubing and the surrounding subsurface strata.

A further object is to provide scale treating composition for use inpreventing the build-up of scale deposits in the well tubing, producingequipment, the bore hole and surrounding strata.

A still further object of this invention is to provide a method of andcomposition for the treatment of gas and oil well tubing and the likecontaining sulfate scale therein to prevent and/or inhibit the build-upof further scale deposits in the tubing.

These as Well as other objects are accomplished according to the presentinvention which comprises a scale prevention and/or inhibitioncomposition comprising a quaternary ammonium compound having the generalformula wherein R is an alkyl radical containing 8 to 20 carbon atoms,and A is an anion selected from the group consisting of halide, acetate,sulfate, nitrate and hydroxide, and mixtures thereof, said treatingcomposition being employed in an amount sufficient to inhibit thedevelopment of scale in an aqueous system. In the above formula thepoint of attachment of the alkyl radical to the nitrogen atom may be atthe 1 or 2 position of the carbon chain. The term alkyl includes alkenyland alkadienyl.

The invention also comprises a method of treating equipment susceptibleto the development of scale deposits therein such as water storage tanksand the like, particularly oil field equipment, using the scaleprevention composition.

Representative quaternary ammonium compounds include trimethyl 1methyl-n-pentadecylammonium chloride, trimethyl-n-octadecylammoniumbromide, trimethyll-methyl-n-nonadecylammonium acetate,trimethyl-n-octylammonium hydroxide, trimethyl-n-dodecylammoniumnitrate, and trimethyl-n-decylammonium sulfate.

In carrying out one aspect of the present invention the method thereofcomprises introducing the scale prevention composition into theequipment to be protected, such as oil well tubing, in the form of anaqueous solution in an amount sufiicient to provide the quaternaryammonium compound therein at a concentration of from about 0.0002 toabout 0.004% by weight and maintaining the scale treating composition incontact with the internal surfaces thereof therein for a contact timesufficient to prevent and/or inhibit the development of scale depositsor additional scale deposits therein. It is desirable to circulate thescale prevention composition through the system to provide adequatecontact of the composition with the surfaces to be protected.Underground strata surrounding the well bore can be treated in a likemanner, i.e. by passing the solution into said strata such as byinjection of the solution down through the bore hole or productiontubing, preferably under pressure.

In general, it has been found that excellent protection againstobjectionable scale deposits can be obtained by maintaining the treatingcomposition in contact with the scale for a contacting time period offrom about 2 to 24 hours and preferably between about 4 to 12 hours.This contacting time period can also be advantageously used in areascontaining some scale deposits such as oil field tubing to prevent orinhibit the build-up of additional scale deposits therein. In areaswhere heavy scale deposits are present or are likely to be encountered,the

contacting time period can be extended to 24 hours or more Without anyharmful effects. If treatment is carried out at fairly frequentintervals with the composition of the present invention i.e. on asemiweekly or weekly basis, then shorter contacting times (e.g.averaging about 4 to 1012 hours) can be used. Less frequent treatingintervals, i.e. at about every 10 or 15 days generally necessitatecorresponding longer contacting times that may average between 12 and 24hours.

The scale prevention composition of the present invention is used in anamount sufiicient to provide to the treating solution the quaternaryammonium compound in an amount of from 0.0002 to 0.004% by weight. Ithas been found that excellent results are obtained with the compound atconcentrations in the range of from about 0.00025 to 0.001% by weight.Higher concentrations (above about .004%) do not provide improved scaleprotection.

A more complete understanding of the invention will be obtained from thefollowing illustrative examples.

The following procedure was used in the evaluations.

A 1000 milliliter glass beaker was provided with sufficient calciumsulfate and sodium chloride, obtained by mixing solutions of calciumchloride and sodium sulfate, to produce an aqueous concentration thereofof 10,000 p.p.m. of calcium sulfate and 50,000 p.p.m. of sodiumchloride. A metal rotor attached to an externally provided mechanicalstirring device was immersed in the test solution for a 24 hour timeperiod. The solution was maintained at a temperature of 104 F. duringthe test period. At the end of the 24 hours, the rotor was removed fromthe solution and from the stirrer, the scale deposited thereon removed,dried and weighed. In all, several tests were conducted on each materialbeing evaluated and the average of the tests was taken as the amount ofscale deposit. The above laboratory test procedure affords goodcorrelation between the results thereby obtained and larger scale fieldevaluations of scale preventing compositions.

The following table records the results of the tests.

TAB LE Average Weight of scale (grams) 1 Additive A is a 50% by weightaqueous solution of a mixture quaternary trimethylalkylammoniumchlorides containing in the alkyl portion from 15 to 20 carbon atoms,wherein the alkyl radical is attached to the nitrogen atom at the 2position.

Additive B is a 50% by weight aqueous solution of a mixture ofquaternary trimethyl-n-alkyl ammonium chlorides containing in the alkylportion from 8 to 18 carbon atoms. The alkyl radicals in the mixture arepresent in the following amounts: oetyl. 8%; decyl, 9%; dodecyl, 47%;tetradccyl, 18%; hexadecyl, 8%; octadecyl, and octadecenyl, 5%.

3 Additive C is a 50% by weight aqueous solution of a mixture ofquaternary trimethyl-n-alkyl ammonium chlorides containing in the alkylportion from 16 to 18 carbon atoms. The alkyl radicals in the mixtureare present in the following amounts: hexadecyl, octadecyl, 10%;octadecenyl, 35%; and octadecadienyl, 45%.

4 Additive D is quaternary trimethylhexadecylammonium bromide (100%concentration).

From the data presented in the above table, it is evident that thequaternary ammonium compounds of the present invention are effectivecalcium sulfate scale inhibitors at low concentrations.

Obviously, other modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore, only such limitations should be imposed asare indicated in the appended claims.

I claim:

1. A method of controlling the build-up of scale deposits selected fromthe group consisting of calcium sulfate scale and barium sulfate scalein an aqueous system which comprises incorporating in said system ascale treating composition consisting essentially of a quaternarytrimethylakylammonium compound having the general formula t R-lf-OHS CH3wherein R is an alkyl radical containing 8 to 20 carbon atoms, and A isan anion selected from the group consisting of halide, acetate, sulfate,nitrate and hydroxide, including mixtures thereof, said treatingcomposition being employed in an amount sufficient to inhibit thedevelopment of scale in an aqueous system.

2. Method as claimed in claim 1 wherein said quaternary ammoniumcompound comprises a ,mixture of quaternary trimethylalkylammoniumcompounds wherein the alkyl radicals vary from 15 to 20 carbon atomseach.

3. Method as claimed in claim 2 wherein the mixture consists of about10% hexadecyl, about 10% actadecyl, about 35% octadecenyl and about 45%octadecadienyl radicals.

4. Method as claimed in claim 2 wherein the mixture consists of about 8%octyl, 9% dccyl, 47% dodecyl, 18% tetradecyl, 8% hexadecyl, 5% octadecyland 5% octadecenyl radicals.

5. Method as claimed in claim 1 wherein said quaternary ammoniumcompound is trimethylhexadecylammonium bromide.

6. Method as claimed in claim 1 wherein said quaternary ammoniumcompound is present in said system in an amount of from about 0.0002 to0.004% by weight.

7. Method as claimed in claim 1 wherein said quaternary ammoniumcompound is present in said system in an amount of from about 0.00025 to0.001% by weight.

References Cited UNITED STATES PATENTS 2,692,231 lO/l954 Stayner et al.2528.55X 2,917,428 12/1959 Hitzman 252--8.55X 3,354,094 11/1967 Brink etal. 252 3,467,192 9/1969 Nolan et al. 2l058X 3,481,869 12/1969 Jones2528.55X 3,488,289 1/1970 Tate 210-58X HERBERT B. GUYNN, PrimaryExaminer U.S. Cl. X.R. 2528.55, 180

